Preparations are picking up for the big lift of Bertha’s damaged front end, even though the Seattle Tunnel Partners project manager says he doesn’t have a new figure for how much repairs and delays might ultimately cost.
Repair work is picking up, so to speak, at tunnel-boring machine Bertha, where contractors want to hoist the damaged machine’s 4-million-pound front end to the surface by late March.
Drilling of the Highway 99 tunnel would resume in August, if the rescue of the long-stranded machine goes smoothly.
“But that’s a pretty aggressive schedule, that’s assuming everything goes right,” said project manager Chris Dixon, of Seattle Tunnel Partners (STP). “And like I’ve said before, the primary objective of all this is that we do the work right and we do it safely. So it’s gonna take as long as it’s gonna take.”
Repairing the tunnel machine
Chris Dixon, project manager for Seattle Tunnel Partners, gave this tentative timeline during an interview Friday:
March: Sever and lift the outer shield, then the 4-million-pound cutter drive, to street level.
April: Separate the cutter, bearing assembly, drive motors and other parts.
May: Reassemble the drive parts, including a new bearing and seals. Lower the refurbished front end into the repair vault.
June: Reconnect the drive unit and cylindrical steel shield.
July: Inspections and tests. Repair vault refilled with dirt.
August: Resume tunneling, through the north wall of the concrete-lined repair vault.
One month after digging resumes, Bertha will stop for inspections or adjustments, Dixon said, before continuing beneath the Alaskan Way Viaduct.
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Late last week a small team of workers, preparing for the great lift, walked atop the 57-foot-diameter behemoth while tethered to cables and temporary beams.
Welders are attaching lugs called “pad eyes” to the outer skin, where cables can be strung through holes in the lugs and secured to tall, movable cranes. The machine’s steel exterior then will be sliced into three pieces, to be lifted out of the deep access vault, and set aside next to Elliott Bay.
That will expose the front-end cluster, including the ring-shaped bearing, the ruined bearing seals, the drive shaft and disc-shaped cutting face.
Other workers are laboring inside Bertha, disconnecting hoses and wires, Dixon said. The bottom eight of its 24 high-voltage drive motors, each 8,000 pounds, have already been disconnected, so that they don’t bang other machine parts while being lifted up. Clearances within the machine and pit really are that tight.
Groundwater is trickling into the vault in amounts that are easily pumped away.
When Bertha pushed through a concrete wall and into the open air of the repair vault last month, STP defended against water leaks by drilling small holes in some rings of the new tunnel wall, and injecting grout from the inside out, Dixon said. More grout was pumped into the soil, from the surface. Grout sealed the small gap between the machine and the hole it carved into the thick concrete vault.
No new dollar estimate
Dixon didn’t have a new figure when asked how much the repairs and delays, first estimated at $125 million, might ultimately cost.
To date, change-order requests are $210 million. These include a longshore labor dispute over which workers would load excavated dirt onto barges; efforts to deal with groundwater in the machine’s Sodo launch pit; and minor changes in where tunnel entrance ramps are positioned.
Recent requests include $12 million to pay for unexpected soil conditions near the base of the repair vault. Dixon said Friday that the bottom layer, shown as impervious clay in state records, turned out to be porous sands and gravel, so contractors needed to relieve groundwater pressure through extra pumping.
The pumping operation is believed to have caused settlement of 1¼ inches at the Alaskan Way Viaduct, and to a Western Avenue water main.
Hitachi-Zosen, which manufactured Bertha, is fronting the money to lift and fix the front end, in an agreement separate from the official warranty, Dixon said. Construction partners Tutor-Perini and Dragados USA are underwriting the 120-foot deep repair vault.
It could take years of legal disputes for the final costs to be divided between STP and the Washington State Department of Transportation, which says there’s currently $140 million in contingency money remaining in the state’s tunnel budget.
Another question is the STP’s financial burn rate — the companies’ spending may soon exceed what the state gives in monthly payments, if it hasn’t occurred already.
The state has paid out roughly $1 billion of the $1.35 billion contract, for the north and south entrances as well as the four-lane highway tunnel that will replace the Alaskan Way Viaduct.
Three years to go
But the job still has almost three years left, far beyond the original goal of opening to traffic in December 2015.
Dixon insists the companies and their machine will see this job through.
“We believe that it’s going to be in such a state of readiness, that we won’t have any more issues tunneling toward South Lake Union.”
He said crews have continued nonstop to build the north and south entrances, as well as the rescue shaft. “Giving up isn’t part of our vocabulary,” he said.
The Seattle operation is the biggest, and probably the most difficult tunnel-machine repair ever attempted, Dixon said.
STP has already proved it could get Bertha into the vault, despite many skeptics who said the machine might fail to make it through.
“We were able to do that without any issues or problems, so we’re very confident that the repairs are going to be successful, so we’re going to complete the tunnel drive.”
Mammoet, the company which built a huge red lift tower next to the Alaskan Way Viaduct, will hold meetings with STP on Monday to discuss details, such as the very slow speed at which the cutter drive will be picked up from the vault floor.
The repair itself qualifies as a megaproject.
Hitachi drawings show that a platform of steel sheets must be laid upon the ground next to the pit, so the surface won’t buckle when the cutter assembly is laid down.
The repair tasks include carving some bigger openings in the cutter head, so soil tumbles more easily into the conveyor system. In December 2013, when the machine overheated and work was halted, it was having trouble scouring and moving soil.
Mixing arms behind the cutting face will be lengthened, to stir more of the incoming dirt and mud on the way to the conveyor.
Steel rods and plates will reinforce the new, heavier bearing. Other steel will reinforce the whole front end — where the bearing unit will be attached to the wall, in an effort to add stability.
“We’re going to have a different machine going forward,” he said, “than the one that broke into the shaft.”
Even after Bertha restarts, it’s still officially in a testing mode for 300 feet, before stopping short of the viaduct for adjustments. Then it would dive into the downtown hillside.
A crucial job this fall will be coping with the soft fill soil above Bertha as it travels near the waterfront, Dixon said. Tunneling crews must carefully measure the soil loss, to avoid settlement or sinkholes. In past years, voids formed above smaller tunnel drills in the Brightwater sewer tunnel and the Beacon Hill light-rail tunnel.
As the machine digs beyond the viaduct, it would enter firmly packed glacial soils. At that point, Dixon said, it ought to reach the full speed of 6 feet per hour.
Bertha has traveled 1,083 feet along its 9,270-foot route since July 30, 2013.